1. Field of the Invention:
This invention relates to silver halide emulsions used to prepare photographic elements having improved speed. This invention especially relates to fine grain emulsions having low fog and good contrast.
2. Description of the Prior Art:
There are a host of silver halide emulsion sensitizers known in the prior art. These include, for example, both inorganic and organic sulfur compounds. Many of these compounds increase emulsion speed but also have a deleterious affect on fog. This is especially true with finer grain emulsions designed to increase covering power and contrast, for example. Thus, there is a pressing need to find chemical sensitizers for fine grain photographic emulsions, for example, that increase emulsion or film speed without reducing covering power or gradient, or increasing fog. The use of certain organic sulfur containing compounds such as the napthol sulfonates are known in the prior art. Most of these prior art references require that the alkali metal or ammonium salt of napthol sulfonates be prepared therefor and then that these compounds be added to the requisite emulsion in an organic solvent. Of course, the use of organic solvents in aqueous silver halide systems is highly undesirable in most instances. Additionally, there is no teaching in the prior art of the addition of specific napthol sulfonates in an aqueous medium to a photographic emulsion to increase the speed thereof.